diff --git a/src/key.cpp b/src/key.cpp
index 803c1b552407..84a068d71454 100644
--- a/src/key.cpp
+++ b/src/key.cpp
@@ -156,21 +156,21 @@ bool CKey::Check(const unsigned char *vch) {
 }
 
 void CKey::MakeNewKey(bool fCompressedIn) {
+    MakeKeyData();
     do {
-        GetStrongRandBytes(keydata);
-    } while (!Check(keydata.data()));
-    fValid = true;
+        GetStrongRandBytes(*keydata);
+    } while (!Check(keydata->data()));
     fCompressed = fCompressedIn;
 }
 
 bool CKey::Negate()
 {
-    assert(fValid);
-    return secp256k1_ec_seckey_negate(secp256k1_context_sign, keydata.data());
+    assert(keydata);
+    return secp256k1_ec_seckey_negate(secp256k1_context_sign, keydata->data());
 }
 
 CPrivKey CKey::GetPrivKey() const {
-    assert(fValid);
+    assert(keydata);
     CPrivKey seckey;
     int ret;
     size_t seckeylen;
@@ -183,7 +183,7 @@ CPrivKey CKey::GetPrivKey() const {
 }
 
 CPubKey CKey::GetPubKey() const {
-    assert(fValid);
+    assert(keydata);
     secp256k1_pubkey pubkey;
     size_t clen = CPubKey::SIZE;
     CPubKey result;
@@ -209,7 +209,7 @@ bool SigHasLowR(const secp256k1_ecdsa_signature* sig)
 }
 
 bool CKey::Sign(const uint256 &hash, std::vector<unsigned char>& vchSig, bool grind, uint32_t test_case) const {
-    if (!fValid)
+    if (!keydata)
         return false;
     vchSig.resize(CPubKey::SIGNATURE_SIZE);
     size_t nSigLen = CPubKey::SIGNATURE_SIZE;
@@ -250,7 +250,7 @@ bool CKey::VerifyPubKey(const CPubKey& pubkey) const {
 }
 
 bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig) const {
-    if (!fValid)
+    if (!keydata)
         return false;
     vchSig.resize(CPubKey::COMPACT_SIGNATURE_SIZE);
     int rec = -1;
@@ -273,10 +273,12 @@ bool CKey::SignCompact(const uint256 &hash, std::vector<unsigned char>& vchSig)
 }
 
 bool CKey::Load(const CPrivKey &seckey, const CPubKey &vchPubKey, bool fSkipCheck=false) {
-    if (!ec_seckey_import_der(secp256k1_context_sign, (unsigned char*)begin(), seckey.data(), seckey.size()))
+    MakeKeyData();
+    if (!ec_seckey_import_der(secp256k1_context_sign, (unsigned char*)begin(), seckey.data(), seckey.size())) {
+        ClearKeyData();
         return false;
+    }
     fCompressed = vchPubKey.IsCompressed();
-    fValid = true;
 
     if (fSkipCheck)
         return true;
@@ -297,22 +299,21 @@ bool CKey::Derive(CKey& keyChild, ChainCode &ccChild, unsigned int nChild, const
         BIP32Hash(cc, nChild, 0, begin(), vout.data());
     }
     memcpy(ccChild.begin(), vout.data()+32, 32);
-    memcpy((unsigned char*)keyChild.begin(), begin(), 32);
+    keyChild.Set(begin(), begin() + 32, true);
     bool ret = secp256k1_ec_seckey_tweak_add(secp256k1_context_sign, (unsigned char*)keyChild.begin(), vout.data());
-    keyChild.fCompressed = true;
-    keyChild.fValid = ret;
+    if (!ret) keyChild.ClearKeyData();
     return ret;
 }
 
 EllSwiftPubKey CKey::EllSwiftCreate(Span<const std::byte> ent32) const
 {
-    assert(fValid);
+    assert(keydata);
     assert(ent32.size() == 32);
     std::array<std::byte, EllSwiftPubKey::size()> encoded_pubkey;
 
     auto success = secp256k1_ellswift_create(secp256k1_context_sign,
                                              UCharCast(encoded_pubkey.data()),
-                                             keydata.data(),
+                                             keydata->data(),
                                              UCharCast(ent32.data()));
 
     // Should always succeed for valid keys (asserted above).
@@ -322,7 +323,7 @@ EllSwiftPubKey CKey::EllSwiftCreate(Span<const std::byte> ent32) const
 
 ECDHSecret CKey::ComputeBIP324ECDHSecret(const EllSwiftPubKey& their_ellswift, const EllSwiftPubKey& our_ellswift, bool initiating) const
 {
-    assert(fValid);
+    assert(keydata);
 
     ECDHSecret output;
     // BIP324 uses the initiator as party A, and the responder as party B. Remap the inputs
@@ -331,7 +332,7 @@ ECDHSecret CKey::ComputeBIP324ECDHSecret(const EllSwiftPubKey& their_ellswift, c
                                           UCharCast(output.data()),
                                           UCharCast(initiating ? our_ellswift.data() : their_ellswift.data()),
                                           UCharCast(initiating ? their_ellswift.data() : our_ellswift.data()),
-                                          keydata.data(),
+                                          keydata->data(),
                                           initiating ? 0 : 1,
                                           secp256k1_ellswift_xdh_hash_function_bip324,
                                           nullptr);
diff --git a/src/key.h b/src/key.h
index 0a7b7569709b..c4c713c02f24 100644
--- a/src/key.h
+++ b/src/key.h
@@ -46,57 +46,77 @@ class CKey
         "COMPRESSED_SIZE is larger than SIZE");
 
 private:
-    //! Whether this private key is valid. We check for correctness when modifying the key
-    //! data, so fValid should always correspond to the actual state.
-    bool fValid{false};
+    /** Internal data container for private key material. */
+    using KeyType = std::array<unsigned char, 32>;
 
     //! Whether the public key corresponding to this private key is (to be) compressed.
     bool fCompressed{false};
 
-    //! The actual byte data
-    std::vector<unsigned char, secure_allocator<unsigned char> > keydata;
+    //! The actual byte data. nullptr for invalid keys.
+    secure_unique_ptr<KeyType> keydata;
 
     //! Check whether the 32-byte array pointed to by vch is valid keydata.
     bool static Check(const unsigned char* vch);
 
+    void MakeKeyData()
+    {
+        if (!keydata) keydata = make_secure_unique<KeyType>();
+    }
+
+    void ClearKeyData()
+    {
+        keydata.reset();
+    }
+
 public:
-    //! Construct an invalid private key.
-    CKey()
+    CKey() noexcept = default;
+    CKey(CKey&&) noexcept = default;
+    CKey& operator=(CKey&&) noexcept = default;
+
+    CKey& operator=(const CKey& other)
     {
-        // Important: vch must be 32 bytes in length to not break serialization
-        keydata.resize(32);
+        if (other.keydata) {
+            MakeKeyData();
+            *keydata = *other.keydata;
+        } else {
+            ClearKeyData();
+        }
+        fCompressed = other.fCompressed;
+        return *this;
     }
 
+    CKey(const CKey& other) { *this = other; }
+
     friend bool operator==(const CKey& a, const CKey& b)
     {
         return a.fCompressed == b.fCompressed &&
             a.size() == b.size() &&
-            memcmp(a.keydata.data(), b.keydata.data(), a.size()) == 0;
+            memcmp(a.data(), b.data(), a.size()) == 0;
     }
 
     //! Initialize using begin and end iterators to byte data.
     template <typename T>
     void Set(const T pbegin, const T pend, bool fCompressedIn)
     {
-        if (size_t(pend - pbegin) != keydata.size()) {
-            fValid = false;
+        if (size_t(pend - pbegin) != std::tuple_size_v<KeyType>) {
+            ClearKeyData();
         } else if (Check(&pbegin[0])) {
-            memcpy(keydata.data(), (unsigned char*)&pbegin[0], keydata.size());
-            fValid = true;
+            MakeKeyData();
+            memcpy(keydata->data(), (unsigned char*)&pbegin[0], keydata->size());
             fCompressed = fCompressedIn;
         } else {
-            fValid = false;
+            ClearKeyData();
         }
     }
 
     //! Simple read-only vector-like interface.
-    unsigned int size() const { return (fValid ? keydata.size() : 0); }
-    const std::byte* data() const { return reinterpret_cast<const std::byte*>(keydata.data()); }
-    const unsigned char* begin() const { return keydata.data(); }
-    const unsigned char* end() const { return keydata.data() + size(); }
+    unsigned int size() const { return keydata ? keydata->size() : 0; }
+    const std::byte* data() const { return keydata ? reinterpret_cast<const std::byte*>(keydata->data()) : nullptr; }
+    const unsigned char* begin() const { return keydata ? keydata->data() : nullptr; }
+    const unsigned char* end() const { return begin() + size(); }
 
     //! Check whether this private key is valid.
-    bool IsValid() const { return fValid; }
+    bool IsValid() const { return !!keydata; }
 
     //! Check whether the public key corresponding to this private key is (to be) compressed.
     bool IsCompressed() const { return fCompressed; }
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index ea13095ed37f..fb1ef58baa60 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -118,7 +118,7 @@ static RPCHelpMan getnetworkhashps()
 
     ChainstateManager& chainman = EnsureAnyChainman(request.context);
     LOCK(cs_main);
-    return GetNetworkHashPS(!request.params[0].isNull() ? request.params[0].getInt<int>() : 120, !request.params[1].isNull() ? request.params[1].getInt<int>() : -1, chainman.ActiveChain());
+    return GetNetworkHashPS(self.Arg<int>(0), self.Arg<int>(1), chainman.ActiveChain());
 },
     };
 }
@@ -230,12 +230,12 @@ static RPCHelpMan generatetodescriptor()
             "\nGenerate 11 blocks to mydesc\n" + HelpExampleCli("generatetodescriptor", "11 \"mydesc\"")},
         [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
 {
-    const int num_blocks{request.params[0].getInt<int>()};
-    const uint64_t max_tries{request.params[2].isNull() ? DEFAULT_MAX_TRIES : request.params[2].getInt<int>()};
+    const auto num_blocks{self.Arg<int>(0)};
+    const auto max_tries{self.Arg<uint64_t>(2)};
 
     CScript coinbase_script;
     std::string error;
-    if (!getScriptFromDescriptor(request.params[1].get_str(), coinbase_script, error)) {
+    if (!getScriptFromDescriptor(self.Arg<std::string>(1), coinbase_script, error)) {
         throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, error);
     }
 
diff --git a/src/rpc/util.cpp b/src/rpc/util.cpp
index 738a5dea162e..02be3a9b80a4 100644
--- a/src/rpc/util.cpp
+++ b/src/rpc/util.cpp
@@ -525,13 +525,59 @@ UniValue RPCHelpMan::HandleRequest(const JSONRPCRequest& request) const
     if (request.mode == JSONRPCRequest::GET_HELP || !IsValidNumArgs(request.params.size())) {
         throw std::runtime_error(ToString());
     }
+    CHECK_NONFATAL(m_req == nullptr);
+    m_req = &request;
     UniValue ret = m_fun(*this, request);
+    m_req = nullptr;
     if (gArgs.GetBoolArg("-rpcdoccheck", DEFAULT_RPC_DOC_CHECK)) {
         CHECK_NONFATAL(std::any_of(m_results.m_results.begin(), m_results.m_results.end(), [&ret](const RPCResult& res) { return res.MatchesType(ret); }));
     }
     return ret;
 }
 
+using CheckFn = void(const RPCArg&);
+static const UniValue* DetailMaybeArg(CheckFn* check, const std::vector<RPCArg>& params, const JSONRPCRequest* req, size_t i)
+{
+    CHECK_NONFATAL(i < params.size());
+    const UniValue& arg{CHECK_NONFATAL(req)->params[i]};
+    const RPCArg& param{params.at(i)};
+    if (check) check(param);
+
+    if (!arg.isNull()) return &arg;
+    if (!std::holds_alternative<RPCArg::Default>(param.m_fallback)) return nullptr;
+    return &std::get<RPCArg::Default>(param.m_fallback);
+}
+
+static void CheckRequiredOrDefault(const RPCArg& param)
+{
+    // Must use `Arg<Type>(i)` to get the argument or its default value.
+    const bool required{
+        std::holds_alternative<RPCArg::Optional>(param.m_fallback) && RPCArg::Optional::NO == std::get<RPCArg::Optional>(param.m_fallback),
+    };
+    CHECK_NONFATAL(required || std::holds_alternative<RPCArg::Default>(param.m_fallback));
+}
+
+#define TMPL_INST(check_param, ret_type, return_code)       \
+    template <>                                             \
+    ret_type RPCHelpMan::ArgValue<ret_type>(size_t i) const \
+    {                                                       \
+        const UniValue* maybe_arg{                          \
+            DetailMaybeArg(check_param, m_args, m_req, i),  \
+        };                                                  \
+        return return_code                                  \
+    }                                                       \
+    void force_semicolon(ret_type)
+
+// Optional arg (without default). Can also be called on required args, if needed.
+TMPL_INST(nullptr, std::optional<double>, maybe_arg ? std::optional{maybe_arg->get_real()} : std::nullopt;);
+TMPL_INST(nullptr, std::optional<bool>, maybe_arg ? std::optional{maybe_arg->get_bool()} : std::nullopt;);
+TMPL_INST(nullptr, const std::string*, maybe_arg ? &maybe_arg->get_str() : nullptr;);
+
+// Required arg or optional arg with default value.
+TMPL_INST(CheckRequiredOrDefault, int, CHECK_NONFATAL(maybe_arg)->getInt<int>(););
+TMPL_INST(CheckRequiredOrDefault, uint64_t, CHECK_NONFATAL(maybe_arg)->getInt<uint64_t>(););
+TMPL_INST(CheckRequiredOrDefault, const std::string&, CHECK_NONFATAL(maybe_arg)->get_str(););
+
 bool RPCHelpMan::IsValidNumArgs(size_t num_args) const
 {
     size_t num_required_args = 0;
diff --git a/src/rpc/util.h b/src/rpc/util.h
index cbbd8831b283..5e113e992c13 100644
--- a/src/rpc/util.h
+++ b/src/rpc/util.h
@@ -5,6 +5,7 @@
 #ifndef BITCOIN_RPC_UTIL_H
 #define BITCOIN_RPC_UTIL_H
 
+#include <consensus/amount.h>
 #include <node/transaction.h>
 #include <pubkey.h>
 #include <rpc/protocol.h>
@@ -13,14 +14,30 @@
 #include <script/sign.h>
 #include <script/signingprovider.h>
 #include <script/standard.h>
+#include <uint256.h>
 #include <univalue.h>
 #include <util/check.h>
 #include <util/strencodings.h>
 
+#include <cstddef>
+#include <cstdint>
+#include <functional>
+#include <initializer_list>
+#include <map>
+#include <optional>
 #include <string>
+#include <type_traits>
+#include <utility>
 #include <variant>
 #include <vector>
 
+class JSONRPCRequest;
+enum ServiceFlags : uint64_t;
+enum class OutputType;
+enum class TransactionError;
+struct FlatSigningProvider;
+struct bilingual_str;
+
 static constexpr bool DEFAULT_RPC_DOC_CHECK{
 #ifdef RPC_DOC_CHECK
     true
@@ -365,6 +382,44 @@ class RPCHelpMan
     RPCHelpMan(std::string name, std::string description, std::vector<RPCArg> args, RPCResults results, RPCExamples examples, RPCMethodImpl fun);
 
     UniValue HandleRequest(const JSONRPCRequest& request) const;
+    /**
+     * Helper to get a request argument.
+     * This function only works during m_fun(), i.e. it should only be used in
+     * RPC method implementations. The helper internally checks whether the
+     * user-passed argument isNull() and parses (from JSON) and returns the
+     * user-passed argument, or the default value derived from the RPCArg
+     * documention, or a falsy value if no default was given.
+     *
+     * Use Arg<Type>(i) to get the argument or its default value. Otherwise,
+     * use MaybeArg<Type>(i) to get the optional argument or a falsy value.
+     *
+     * The Type passed to this helper must match the corresponding
+     * RPCArg::Type.
+     */
+    template <typename R>
+    auto Arg(size_t i) const
+    {
+        // Return argument (required or with default value).
+        if constexpr (std::is_integral_v<R> || std::is_floating_point_v<R>) {
+            // Return numbers by value.
+            return ArgValue<R>(i);
+        } else {
+            // Return everything else by reference.
+            return ArgValue<const R&>(i);
+        }
+    }
+    template <typename R>
+    auto MaybeArg(size_t i) const
+    {
+        // Return optional argument (without default).
+        if constexpr (std::is_integral_v<R> || std::is_floating_point_v<R>) {
+            // Return numbers by value, wrapped in optional.
+            return ArgValue<std::optional<R>>(i);
+        } else {
+            // Return other types by pointer.
+            return ArgValue<const R*>(i);
+        }
+    }
     std::string ToString() const;
     /** Return the named args that need to be converted from string to another JSON type */
     UniValue GetArgMap() const;
@@ -381,6 +436,9 @@ class RPCHelpMan
     const std::vector<RPCArg> m_args;
     const RPCResults m_results;
     const RPCExamples m_examples;
+    mutable const JSONRPCRequest* m_req{nullptr}; // A pointer to the request for the duration of m_fun()
+    template <typename R>
+    R ArgValue(size_t i) const;
 };
 
 RPCErrorCode RPCErrorFromTransactionError(TransactionError terr);
diff --git a/src/support/allocators/secure.h b/src/support/allocators/secure.h
index 46be5f4876f1..285d0e49965f 100644
--- a/src/support/allocators/secure.h
+++ b/src/support/allocators/secure.h
@@ -59,5 +59,28 @@ struct secure_allocator {
 typedef std::basic_string<char, std::char_traits<char>, secure_allocator<char> > SecureString;
 
 typedef std::vector<unsigned char, secure_allocator<unsigned char> > SecureVector;
+template<typename T>
+struct SecureUniqueDeleter {
+    void operator()(T* t) noexcept {
+        secure_allocator<T>().deallocate(t, 1);
+    }
+};
+
+template<typename T>
+using secure_unique_ptr = std::unique_ptr<T, SecureUniqueDeleter<T>>;
+
+template<typename T, typename... Args>
+secure_unique_ptr<T> make_secure_unique(Args&&... as)
+{
+    T* p = secure_allocator<T>().allocate(1);
+
+    // initialize in place, and return as secure_unique_ptr
+    try {
+        return secure_unique_ptr<T>(new (p) T(std::forward(as)...));
+    } catch (...) {
+        secure_allocator<T>().deallocate(p, 1);
+        throw;
+    }
+}
 
 #endif // BITCOIN_SUPPORT_ALLOCATORS_SECURE_H
diff --git a/src/wallet/rpc/coins.cpp b/src/wallet/rpc/coins.cpp
index 51fd86088526..04a3b795813a 100644
--- a/src/wallet/rpc/coins.cpp
+++ b/src/wallet/rpc/coins.cpp
@@ -197,8 +197,8 @@ RPCHelpMan getbalance()
 
     LOCK(pwallet->cs_wallet);
 
-    const UniValue& dummy_value = request.params[0];
-    if (!dummy_value.isNull() && dummy_value.get_str() != "*") {
+    const auto dummy_value{self.MaybeArg<std::string>(0)};
+    if (dummy_value && *dummy_value != "*") {
         throw JSONRPCError(RPC_METHOD_DEPRECATED, "dummy first argument must be excluded or set to \"*\".");
     }
 
diff --git a/src/wallet/rpc/spend.cpp b/src/wallet/rpc/spend.cpp
index de9385e82b5d..f44eedff2bc8 100644
--- a/src/wallet/rpc/spend.cpp
+++ b/src/wallet/rpc/spend.cpp
@@ -926,7 +926,7 @@ RPCHelpMan send()
             {"options", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED_NAMED_ARG, "",
                 Cat<std::vector<RPCArg>>(
                 {
-                    {"add_inputs", RPCArg::Type::BOOL, RPCArg::Default{false}, "If inputs are specified, automatically include more if they are not enough."},
+                    {"add_inputs", RPCArg::Type::BOOL, RPCArg::DefaultHint{"false when \"inputs\" are specified, true otherwise"},"Automatically include coins from the wallet to cover the target amount.\n"},
                     {"include_unsafe", RPCArg::Type::BOOL, RPCArg::Default{false}, "Include inputs that are not safe to spend (unconfirmed transactions from outside keys and unconfirmed replacement transactions).\n"
                                                           "Warning: the resulting transaction may become invalid if one of the unsafe inputs disappears.\n"
                                                           "If that happens, you will need to fund the transaction with different inputs and republish it."},
@@ -1377,7 +1377,7 @@ RPCHelpMan walletcreatefundedpsbt()
                     {"options", RPCArg::Type::OBJ, RPCArg::Optional::OMITTED_NAMED_ARG, "",
                         Cat<std::vector<RPCArg>>(
                         {
-                            {"add_inputs", RPCArg::Type::BOOL, RPCArg::Default{false}, "If inputs are specified, automatically include more if they are not enough."},
+                            {"add_inputs", RPCArg::Type::BOOL, RPCArg::DefaultHint{"false when \"inputs\" are specified, true otherwise"}, "Automatically include coins from the wallet to cover the target amount.\n"},
                             {"include_unsafe", RPCArg::Type::BOOL, RPCArg::Default{false}, "Include inputs that are not safe to spend (unconfirmed transactions from outside keys and unconfirmed replacement transactions).\n"
                                                           "Warning: the resulting transaction may become invalid if one of the unsafe inputs disappears.\n"
                                                           "If that happens, you will need to fund the transaction with different inputs and republish it."},
diff --git a/src/wallet/rpc/wallet.cpp b/src/wallet/rpc/wallet.cpp
index cd9740c8ab1f..019b9350319b 100644
--- a/src/wallet/rpc/wallet.cpp
+++ b/src/wallet/rpc/wallet.cpp
@@ -765,7 +765,7 @@ static RPCHelpMan unloadwallet()
         // Release the "main" shared pointer and prevent further notifications.
         // Note that any attempt to load the same wallet would fail until the wallet
         // is destroyed (see CheckUniqueFileid).
-        std::optional<bool> load_on_start = request.params[1].isNull() ? std::nullopt : std::optional<bool>(request.params[1].get_bool());
+        std::optional<bool> load_on_start{self.MaybeArg<bool>(1)};
         if (!RemoveWallet(context, wallet, load_on_start, warnings)) {
             throw JSONRPCError(RPC_MISC_ERROR, "Requested wallet already unloaded");
         }
diff --git a/test/functional/wallet_fundrawtransaction.py b/test/functional/wallet_fundrawtransaction.py
index f97b54ecec09..92b5921378ff 100755
--- a/test/functional/wallet_fundrawtransaction.py
+++ b/test/functional/wallet_fundrawtransaction.py
@@ -103,6 +103,7 @@ def run_test(self):
         self.generate(self.nodes[2], 1)
         self.generate(self.nodes[0], 121)
 
+        self.test_add_inputs_default_value()
         self.test_change_position()
         self.test_simple()
         self.test_simple_two_coins()
@@ -1021,6 +1022,120 @@ def test_external_inputs(self):
 
         self.nodes[2].unloadwallet("extfund")
 
+    def test_add_inputs_default_value(self):
+        self.log.info("Test 'add_inputs' default value")
+
+        # Create and fund the wallet with 5 BTC
+        self.nodes[2].createwallet("test_preset_inputs")
+        wallet = self.nodes[2].get_wallet_rpc("test_preset_inputs")
+        addr1 = wallet.getnewaddress()
+        self.nodes[0].sendtoaddress(addr1, 5)
+        self.generate(self.nodes[0], 1)
+
+        # Covered cases:
+        # 1. Default add_inputs value with no preset inputs (add_inputs=true):
+        #       Expect: automatically add coins from the wallet to the tx.
+        # 2. Default add_inputs value with preset inputs (add_inputs=false):
+        #       Expect: disallow automatic coin selection.
+        # 3. Explicit add_inputs=true and preset inputs (with preset inputs not-covering the target amount).
+        #       Expect: include inputs from the wallet.
+        # 4. Explicit add_inputs=true and preset inputs (with preset inputs covering the target amount).
+        #       Expect: only preset inputs are used.
+        # 5. Explicit add_inputs=true, no preset inputs (same as (1) but with an explicit set):
+        #       Expect: include inputs from the wallet.
+
+        # Case (1), 'send' command
+        # 'add_inputs' value is true unless "inputs" are specified, in such case, add_inputs=false.
+        # So, the wallet will automatically select coins and create the transaction if only the outputs are provided.
+        tx = wallet.send(outputs=[{addr1: 3}])
+        assert tx["complete"]
+
+        # Case (2), 'send' command
+        # Select an input manually, which doesn't cover the entire output amount and
+        # verify that the dynamically set 'add_inputs=false' value works.
+
+        # Fund wallet with 2 outputs, 5 BTC each.
+        addr2 = wallet.getnewaddress()
+        source_tx = self.nodes[0].send(outputs=[{addr1: 5}, {addr2: 5}], options={"change_position": 0})
+        self.generate(self.nodes[0], 1)
+
+        # Select only one input.
+        options = {
+            "inputs": [
+                {
+                    "txid": source_tx["txid"],
+                    "vout": 1  # change position was hardcoded to index 0
+                }
+            ]
+        }
+        assert_raises_rpc_error(-4, "Insufficient funds", wallet.send, outputs=[{addr1: 8}], options=options)
+
+        # Case (3), Explicit add_inputs=true and preset inputs (with preset inputs not-covering the target amount)
+        options["add_inputs"] = True
+        options["add_to_wallet"] = False
+        tx = wallet.send(outputs=[{addr1: 8}], options=options)
+        assert tx["complete"]
+
+        # Case (4), Explicit add_inputs=true and preset inputs (with preset inputs covering the target amount)
+        options["inputs"].append({
+            "txid": source_tx["txid"],
+            "vout": 2  # change position was hardcoded to index 0
+        })
+        tx = wallet.send(outputs=[{addr1: 8}], options=options)
+        assert tx["complete"]
+        # Check that only the preset inputs were added to the tx
+        decoded_psbt_inputs = self.nodes[0].decodepsbt(tx["psbt"])['tx']['vin']
+        assert_equal(len(decoded_psbt_inputs), 2)
+        for input in decoded_psbt_inputs:
+            assert_equal(input["txid"], source_tx["txid"])
+
+        # Case (5), assert that inputs are added to the tx by explicitly setting add_inputs=true
+        options = {"add_inputs": True, "add_to_wallet": True}
+        tx = wallet.send(outputs=[{addr1: 8}], options=options)
+        assert tx["complete"]
+
+        ################################################
+
+        # Case (1), 'walletcreatefundedpsbt' command
+        # Default add_inputs value with no preset inputs (add_inputs=true)
+        inputs = []
+        outputs = {self.nodes[1].getnewaddress(): 8}
+        assert "psbt" in wallet.walletcreatefundedpsbt(inputs=inputs, outputs=outputs)
+
+        # Case (2), 'walletcreatefundedpsbt' command
+        # Default add_inputs value with preset inputs (add_inputs=false).
+        inputs = [{
+            "txid": source_tx["txid"],
+            "vout": 1  # change position was hardcoded to index 0
+        }]
+        outputs = {self.nodes[1].getnewaddress(): 8}
+        assert_raises_rpc_error(-4, "Insufficient funds", wallet.walletcreatefundedpsbt, inputs=inputs, outputs=outputs)
+
+        # Case (3), Explicit add_inputs=true and preset inputs (with preset inputs not-covering the target amount)
+        options["add_inputs"] = True
+        options["add_to_wallet"] = False
+        assert "psbt" in wallet.walletcreatefundedpsbt(outputs=[{addr1: 8}], inputs=inputs, options=options)
+
+        # Case (4), Explicit add_inputs=true and preset inputs (with preset inputs covering the target amount)
+        inputs.append({
+            "txid": source_tx["txid"],
+            "vout": 2  # change position was hardcoded to index 0
+        })
+        psbt_tx = wallet.walletcreatefundedpsbt(outputs=[{addr1: 8}], inputs=inputs, options=options)
+        # Check that only the preset inputs were added to the tx
+        decoded_psbt_inputs = self.nodes[0].decodepsbt(psbt_tx["psbt"])['tx']['vin']
+        assert_equal(len(decoded_psbt_inputs), 2)
+        for input in decoded_psbt_inputs:
+            assert_equal(input["txid"], source_tx["txid"])
+
+        # Case (5), 'walletcreatefundedpsbt' command
+        # Explicit add_inputs=true, no preset inputs
+        options = {
+            "add_inputs": True
+        }
+        assert "psbt" in wallet.walletcreatefundedpsbt(inputs=[], outputs=outputs, options=options)
+
+        self.nodes[2].unloadwallet("test_preset_inputs")
     def test_include_unsafe(self):
         self.log.info("Test fundrawtxn with unsafe inputs")